The overall objective of the research program is to develop the yeast, Saccharomyces cerevisiae, as a model system for study of the genetic control of meiosis, with particular emphasis on the development of high recombinational ability and chromosome segregation. the experimental program is aimed at determining 1) the interaction of genes that control the level and distribution of meiotic exchanges, 2) the genetic coordination of chromosomal recombination and segregation and 3) the degree to which genes required for meiotic exchange and segregation function in mitosis. The research involves characterization of the temporal properties of exchange in wild type cells as they progress through meiosis and identification of gene functions required for meiotic recombination by analysis of spo (sporulation-defective), rad (radiation-sensitive) and rec (recombination-defective) mutants. Cytological, genetic, and biochemical landmark meiotic events will be examined in single and multiple mutant combinations. The effects of these mutations on both sister and non-sister chromatid exchange will be studied in a novel haploid meiotic system which bypasses reductional chromosome segregation. This system will also be used to isolate new mutations affecting exchange and segregation. The involvement of meiotic recombination functions in mitotic recombination pathways will be examined by analysis of mitotic crossing over, genetic transformation, and mating-type switching.